fix: reset announceRetryCount in replaceSubagentRunAfterSteer

Address review feedback: the spread operator carries stale retry state
into replacement runs, potentially causing immediate force-expiration
without ever attempting announce delivery.

src/agents/subagent-registry.ts

@@ -436,6 +436,8 @@ export function replaceSubagentRunAfterSteer(params: {
     cleanupCompletedAt: undefined,
     cleanupHandled: false,
     suppressAnnounceReason: undefined,
+    announceRetryCount: undefined,
+    lastAnnounceRetryAt: undefined,
     archiveAtMs,
     runTimeoutSeconds,
   };